Ryan Falcone Hess

Microfabricated Nitrogen-Phosphorus Detector: Chemically Mediated Thermionic Emission

Many chemical warfare agents and toxic industrial chemicals contain nitrogen and phosphorus atoms. Commercially available benchtop Nitrogen-Phosphorus Detectors (NPDs) for gas chromatographs are highly selective for nitrogen and phosphorus compared to carbon. However, the detection mechanism for these thermionic detectors is poorly understood despite 60 years of use. In addition these detectors require the use of flammable gas and operate at high power. We developed a microfabricated NPD (μNPD) with similar selectivity that does not require the use of flammable gas and uses relatively low power. Our μNPD consists of an alkali metal silicate thin film spray coated onto a microhotplate. The silicate thin film is responsible for providing the thermionic emission necessary for analyte detection. We conducted a series of experiments designed to better elucidate the detection mechanism. Our results indicate that surface catalyzed ionization of nitrogen and phosphorus containing analytes is the most likely mechanism.

Development of a downhole tool measuring real-time concentration of ionic tracers and pH in geothermal reservoirs

For enhanced or Engineered Geothermal Systems (EGS) geothermal brine is pumped to the surface via the production wells, the heat extracted to turn a turbine to generate electricity, and the spent brine re-injected via injection wells back underground. If designed properly, the subsurface rock formations will lead this water back to the extraction well as heated brine. Proper monitoring of these geothermal reservoirs is essential for developing and maintaining the necessary level of productivity of the field. Chemical tracers are commonly used to characterize the fracture network and determine the connectivity between the injection and production wells. Currently, most tracer experiments involve injecting the tracer at the injection well, manually collecting liquid samples at the wellhead of the production well, and sending the samples off for laboratory analysis. While this method provides accurate tracer concentration data at very low levels of detection, it does not provide information regarding the location of the fractures which were conducting the tracer between wellbores. Sandia is developing a high-temperature electrochemical sensor capable of measuring tracer concentrations and pH downhole on a wireline tool. The goal of this effort is to collect real-time pH and ionic tracer concentration data at temperatures up to 225 °C and pressures up to 3000 psi. In this paper, a prototype electrochemical sensor and the initial data obtained will be presented detailing the measurement of iodide tracer concentrations at high temperature and pressure in a newly developed laboratory scale autoclave.

Scandium separation from tungsten crucibles

The first step in an attempt to isolate Sco from a Wo crucible was explored by soaking the samples in a series of organic (HOAc) and inorganic (HCl, H2SO4, H3PO4, HNO3) acids. All samples, except the HOAc, yielded a powder. The weight loss suggests that HNO3 is the most efficient solvent; however, the powders were tentatively identified by PXRD and found to contain both W and Sc by-products. The higher weight loss may also indicate dissolution of the Wo crucible, which was further evidenced upon visual inspection of the crucible. The H3PO4 acid soak yielded the cleanest removal of Sc from the crucible. More work to understand the separation of the Sco from the Wo crucible is necessary but the acid routes appear to hold promise under not as of yet established criteria.